It has long been known in the disposable absorbent bandage are that it is extremely desirable to construct absorptive devices, such as disposable diapers, sanitary napkins, and the like, presenting a dry surface feel to the user to improve wearing comfort and to minimize the development of undesirable skin conditions due to prolonnged exposure to moisture absorbed within the bandage. One viable prior art solution to the aforementioned problem is disclosed in U.S. Pat. No. 4,041,951 issued to Sanford on Aug. 16, 1977 and hereby incorporated herein by reference. The Sandford patent discloses a preferred disposable diaper structure comprising a substantially planar, moisture absorbent layer disposed between a soft topsheet and a moisture-resistant backing sheet. The nonwoven fibrous topsheet preferably comprises an integral structure containing a multiplicity of depressed areas which intimately contact the uppermost surface of a substantially planar, moisture absorbent layer. The nondepressed areas of the topsheet contact the wearer's skin in-use. In a particularly preferred embodiment, the nonwoven fibrous topsheet is comprised of a substantially hydrophobic material exhibiting wet resilience such that the topsheet tends to resume its substantially three-dimensional character upon removal of pressure applied against the topsheet by the body movements of the wearer. The nondepressed areas of the topsheet, which are of substantially the same density as the depressed areas, tend to isolate the wearer's skin from moisture contained within the moisture absorbent layer, thereby providing surface dryness and resistance to rewetting when the structure is temporarily subjected to pressure resulting from the wearer's body movements.
U.S. Pat. No. 3,814,101 issued to Kozak on June 4, 1974, attacks the problem of a wet topsheet in a manner slightly different from the use of hydrophobic nonwoven materials. Kozak suggests a topsheet of a nonfibrous, hydrophobic film which is provided with a plurality of valvular slits which restrict the reverse flow of liquid from the absorbent element of the device.
U.S. Pat. No. 3,929,135 issued to Thompson on Dec. 30, 1975, and hereby incorporated herein by reference, suggests a topsheet comprised of liquid-impermeable material, but provided with tapered capillaries, said capillaries having a base opening in the plane of the topsheet and an apex opening remote from the plane of the topsheet, said apex opening being in intimate contact with the absorbent pad utilized in the disposable absorbent bandage. The topsheet disclosed in the Thompson patent allows the free transfer of fluids from the body into the absorbent element of the device while inhibiting the reverse flow of these fluids, thereby providing a relatively much drier surface in contact with the user than had been previously obtainable. However, contrary to expectations, it has been learned that despite the highly effective fluid transfer and fluid isolation characteristics exhibited by plastic topsheets of the type generally disclosed in the Thompson patent and their proven compatibility with the wearer's skin, many users find it psychologically undesirable to employ a material which is perceivably plastic in contact with their skin. It is believed that this user reaction is due partly to the highly regulated tapered capillary pattern on the wearer-contacting surface of the topsheet and partly to the glossy appearance of the film. Users are prone to view both of these characteristics negatively when dealing with plastic films which will contact the user's skin.
Prior art method and apparatus for embossing, vacuum forming and/or perforating plastic film have substantially precluded the elimination of such plastic characteristics exhibited by formed films. U.S. Pat. No. 2,809,392 issued to Armstrong on Oct. 15, 1957 discloses a prior art vacuum forming drum utilized to emboss a heat softened thermoplastic film drawn across its surface. The vacuum drum comprises a rolled hollow shell provided with a plurality of circumferential grooves which are positioned progressively closer together toward the ends of the drum. Holes about 1/16 inch in diameter are drilled through the shell at circumferentially spaced points in the grooves. The heat softened film is embossed by the application of vacuum to the interior surfaces of the drum while the film is in contact with the peripery thereof. As should be clear from the foregoing, the pattern of emboss is inherently governed by machining limitations utilized in constructing the drum.
U.S. Pat. No. Re. 23,910 issued to Smith et al. on Dec. 14, 1954 discloses yet another prior art method and apparatus for producing textured plastic films. The Smith et al. patent suggests the use of a suction box located beneath the surface of a woven wire mesh to draw a heat softened plastic film into conformity with the woven wire mesh. The patent further suggests that a specially patterned belt or fabric could be employed to deform the film in its own likeness by supporting the belt or fabric on the woven wire mesh. In yet another embodiment, the process is carried out utilizing the cylindrical surface of a drum. Nonetheless, the patterns which can be imparted to the film are governed by weaving limitations in the case of the woven wire and fabric and machining/punching limitations in the case of the patterned belt or drum. Furthermore, it is preferred, according to the teachings of Smith et al., that the forming belt and the forming drum be utilized to produce discrete lengths of film rather than continuous webs in order to avoid creating joint marks where the ends of the belt or the ends of the drum are joined together.
U.S. Pat. No. 3,054,148 issued to Zimmerli on Sept. 18, 1962 discloses a process for producing a perforated plastic sheet. The process comprises subjecting a plasticized plastic sheet or film to the action of pressure over a perforated support or molding element. The softened plastic material is caused to flow into the perforations of the molding element to a depth which can be regulated by control of such factors as the degree of softness of the material, the direction of pressure flow and the relative thickness of the plastic sheet. The molding element preferably comprises a drum which may be made from a metal sheet having the perforated design stamped or otherwise cut from the sheet. However, in the production of simulated fabrics or woven materials, the molding element preferably comprises a woven wire mesh.
A particularly preferred method for continuously debossing and, if desired, perforating a plastic film is disclosed in the commonly assigned co-pending patent application of Malcolm B. Lucas and Robert H. Van Coney entitled "METHOD OF AND APPARATUS FOR DEBOSSING AND PERFORATING A RUNNING RIBBON OF THERMOPLASTIC FILM", U.S. Ser. No. 733,961, filed Oct. 19, 1976, issued on Apr. 24, 1979 as U.S. Pat. No. 4,151,240, and hereby incorporated herein by reference. The Lucas et al. application which, in a preferred embodiment, discloses means for forming a plastic film exhibiting a regulated pattern of tapered capillaries as generally disclosed in the aforementioned patent to Thompson, causes a ribbon of planar thermoplastic film to be forwarded from a supply roll, thence about a circumferentially extending portion of a rotating debossing/perforating cylinder and then downstream where the debossed and perforated film may be further processed or wound on a spool to form a roll. The debossing/perforating cylinder preferably comprises a perforated tubular member through which a plurality of independently adjustable levels of vacuum can be applied from within the cylinder to circumferentially spaced sections of the film in contact with the exterior surface of the perforated tubular member. The apparatus further causes a virtual curtain of hot air to be directed radially inwardly towards a predetermined zone of the perforated tubular member. Thus, vacuum applied from within the cylinder acts in concert with the curtain of hot air which flash heats the film sufficiently to effect debossing and perforating of the film running circumferentially about the rotating cylinder. The apparatus may further control tension in the film both upstream and downstream of the debossing cylinder at predetermined constant levels. The disclosed method for making the perforated tubular forming member preferably entails forming the member inside out by electrodepositing nickel about the exterior surfaces of a pattern cylinder having outwardly extending conical projections located about its periphery, and then turning it right side out by slitting it longitudinally, reverse rolling it into the desired tubular shape, and seaming it along the edges thus formed. From the foregoing it is clear that, even in this preferred film forming process, the particular shape or pattern imparted to the thermoplastic film on the surface of the forming cylinder is indirectly governed by limitations inherent in the machining or metal displacing processes utilized to form the pattern cylinder.
Accordingly, it is an object of the present invention to provide a plastic web exhibiting a three-dimensional pattern of embossments and/or perforations or any desired combination thereof which is independent of the machining and weaving limitations inherent in prior art forming surfaces.
It is another object of the present invention to provide a forming surface exhibiting nearly any desired three-dimensional structure at a scale so fine that the resultant plastic sheets formed thereon exhibit fiber-like properties and characteristics.
It is another object of the present invention to provide a continuous, three-dimensionally patterned forming surface, the ends of which may, if desired, be secured to one another substantially without disruption to the three-dimensional pattern contained therein.
It is yet another object of the present invention to provide a forming surface exhibiting a degree of surface roughness or texture to further aid in reducing the glossy appearance typically exhibited by plastic films.
It is still another object of the present invention to provide a fluid-pervious plastic web exhibiting a fiber-like appearance and tactile impression, i.e, an overall impression of softness, said web further exhibiting a fine scale three-dimensional microstructure comprising a regulated continuum of capillary networks, preferably of steadily decreasing size, originating in and extending from one surface of said film and terminating in the form of apertures in the opposite surface thereof to promote rapid liquid transport in the direction of decreasing capillary size. As utilized herein, the term "microstructure" refers to a structure of such fine scale that its precise detail is readily perceived by the human eye only upon magnification by microscopic or other means well known in the art. The term "fiber-like", as utilized herein to describe the appearance of plastic webs of the present invention, refers generally to any fine scale pattern of debossments or apertures, random or non-random, reticulated or non-reticulated, which connotes an overall appearance and impression of a woven or non-woven fibrous web when viewed by the human eye.